I'm the Robin Hood of Skyrim !
I love Archery...
I think it's just practice...
Mostly i can do 1 hit kill or then hit a moving target... but as you said, you gotta calculate a little and not just Spam arrows in the enemy..
Example: If the target is running left, try to aim in front of him, on the direction he is running, so the timing the arrow gets there and the target runs there wil be perfect and you'll kill...
Example: 2 If the target is walking left, same thing but aim a little bit near than when he is running.. etc
Perhaps i could give you a few tips if you want, when i have more time.. =]
But here is the major hint, don't spam arrows, be patient and kinda calculate your shots and try to foresee the target's next movement. ;D
EDIT: Another major tip.. pick the perks that allow you to zoom and the other one that when you zoom, the game slows down 50% or 25% .. it gets sooo much easier.
EDIT 2: As SouLosT said, if you are a Sneak type character, then archery will be easy, because you'll be able to get close enought to shoot.. =]